requireFunctionLike
function requireFunctionLike( value: unknown, message: string = "Expected a function." // eslint-disable-next-line @typescript-eslint/no-unsafe-function-type ): Function;
The cheap test — typeof value === "function" — which is what you want before calling something. isFunction is the stricter reading of the same question.
isX and nonX answer a question and never interrupt control flow; requireX and requireNonX hand the value back or throw. The scheme is explained in Validation conventions.
Parameters
Parameter | Type | Description |
|---|---|---|
|
| The value to validate. |
|
| The message of the exception. A default is used when omitted. |
Returns
Function — the same value, typed as a callable value.
Throws
Exception | Condition |
|---|---|
| the value is not callable. |
Examples
What passes and what does not
requireFunctionLike(function () {}); // => function () {}
requireFunctionLike(Math.max); // => Math.max
requireFunctionLike(null); // throws IllegalArgumentException
requireFunctionLike({}); // throws IllegalArgumentException
See also
Source
23 September 2026
This documentation was generated with AI (Claude) from the library's source code.